Method of removing starch size from cellulose fabric with aqueous alkaline medium containing alkali metal bromites, alkali metal hypobromites, or mixtures thereof



iz-lifiini METHOD OF REMOVING STARCH SIZE FROM CELLULOSE FABRIC WITH AQUEOUS ALKA- LINE MEDIUM CONTAINING ALKALI METAL BROMITES, ALKALI METAL HYPOBROMITES, 0R MIXTURES THEREOF Jacqueline Leclerc, Paris, France, assignor to Societe dEtudes Chimiques Pour llndustrie et lAgriculture, Paris, France, a society of France No Drawing. Filed July 8, 1957, Ser. No. 670,397 Claims priority, application France July 10, 1956 6 Claims. (Cl. 8138) This invention relates to the manufacture of cellulose fibre fabrics, especially cotton fabrics, and more particularly to a de-sizing treatment preparatory to the finishing operations which include scouring, bleaching and dyeing.

The purpose of the de-sizing or de-starching step is to remove from the fabric amylaceous (starchy) matters that were applied to the Warp of the fabric in order to facilitate weaving. The starch impregnating the fabric interferes seriously with the penetration of the reagents, and thus renders subsequent treatments difiicult to perform efficiently. It is therefore important in the interests of successful bleaching and dyeing results that the fabric be stripped as thoroughly as possible from the starch contained in it. The de-sizing operation according to this invention may be either effected in a separate step prior to scouring or simultaneously with the scouring step.

Various types of processes have heretofore been suggested for removing the size or starch from cellulose fabrics. One method involves the use of acids, especially dilute sulfuric acid, for hydrolyzing the amylaceous substances and making them soluble, but processes based on this method only succeed in partly removing the starch, usually to an inadequate degree.

A more complete removal of the starch is usually accomplished with de-sizing processes involving the use of enzymes, but such processes are generally difficult to operate and control and accordingly possesses grave drawbacks. Thus, such methods require operating in solutions at temperatures above 50 C., and wherein the pH must be held within narrow predetermined ranges. The enzymes moreover are sensitive to certain chemical agents and it is frequently found that various additions introduced into the de-sizing compositions for aiding in the de-sizing action, such as wetters, softeners and antiseptics, acts as poisons or contaminants killing the enzymes and thus seriously hindering successful de-sizing.

One drawback common both to the acidic and enzymatic de-sizing processes is the necessity of storing the fabric impregnated with the de-sizing solution over periods long enough to permit full action of the reagents to take place. During such storage it is a practical im possibility to maintain a uniform and constant temperature throughout the fabric in folded or heaped-up condition this leads to non-uniformity in the de-sizing process and consequent unevenness in the bleaching and dyeing.

De-sizing has also been effected by oxidizing the amylaceous substances with various oxidizing agents. Thus, it has been suggested to perform the de-sizing operation during the scouring step with the use of sodium chlorite as the starch oxidizing agent. Since chlorite has no effect on starch in alkaline media, the removal of the starch during a scouring operation which, precisely, must be conducted in an alkaline medium, is no better in its results than if the operation were conducted in the absence of the chlorite. It has, accordingly, been suggested more recently to carry out the chlorite de-sizing operation in an acid medium and in the presence of water vapour, which of course precludes operation simultaneously with the scouring step. The last mentioned method however has an advantage in that it permits continuous treatment, but the steaming operation is expensive and requires the use of special equipment.

It has now been found that the de-sizing of cellulose fabric can be performed in an especially satisfactory and inexpensive way, through oxidation in an alkaline medium, by means of oxygen derivatives of bromine such as alkali bromites and alkali hypobromites. The use of such reagents results in a total removal of amylaceous substances even in very tight-woven fabrics, in a comparatively short time and operating at ordinary temperatures, while retaining all of the characteristics of the fabric unimpaired. The consumption of reagent is low. While the consumption depends on the reagent use, the following broad ranges may be mentioned by way of indication but not of limitation. For complete size removal from a heavy and tight woven fabric, very difiicult to de-size by conventional methods and containing from 11 to 12% of size, the available bromine concentration in the reagent use according to the invention is only about 5 to 7 grams available bromine per kilogram of dry material, if the de-sizing agent used is bromite, and about 40 grams available bromine if the agent is hypobromite. It will be recalled in this connection that the available bromine concentration in a solution is the sum total of the free bromine content, plus twice the bromine content of the hypobromite in the solution, plus four times the bromine content in the bromite in the solution. Lower reagent consumptions are of course obtained in the case of fabric that is lighter and/ or contains a lower proportion of size than in the example above. It has been found that bromite is definitely more active than hypobromite and such a reagent will be preferably selected in connection with fabrics more difficult to de-size, such as poplin, whereas hypobromite on the other hand, while also suitable for this type of fabric, is preferred for use with fabrics easier to de-size such as calico.

In order to establish comparative data between the efficiency of the reagents of the invention and that of known oxidizing agents, laboratory tests have been carried out on the one hand with oxygen compounds of bromine (sodium hypobromite and bromite) and on the hand with the corresponding oxygen compounds of chlorine (sodium hypochlorite and'chlorite). The table below sums up the results of these tests. All the tests were effected using test samples of a poplin Weighing about grams per square meter and containing about 11.5% size. The elimination of the starch is tested on completion of the treatment, by the iodine testing method, wherein change in colour of the sample from blue to yellow indicates that the starch present has disappeared.

The test results in the above table may be summarized by the statement that at ordinary temperature (20 C.) only sodium hypobromite and bromite are effective, though to different extents.

"ti EOE-t The table further shows that:

The much more efficient reagent bromite can be used in a much more dilute solution and acts faster with a lower reagent consumption.

Sodium hypochlorite has some action at about 50 C., but the tests show that twice as much reagent is then consumed even though the desired result is not attained.

The chlorite is totally ineffective in an alkaline medium, while under the more severe conditions of an acid medium (pH 4 to 5) its action on starch is very slight, at 80 C.

The following point may further be noted concerning the compared actions of oxygen derivatives of bromine and chlorine as size-removers. Bromine derivatives are both active, with the bromine however definitely more potent than the hypobromite. As concerns chlorine derivatives on the other hand, the comparative efficiencies are reversed, i.e. the limited action of the hypochlorite is markedly greater than that of the chlorite.

In carrying the invention into practice, solutions of alkali bromite and/or hypobromite are used, obtained in any appropriate way. The solutions may contain certain quantity of foreign ions without impairing the de-sizing action. Thus, the presence of alkali bromides and bromates, even in comparatively high amounts, is not at all objectionable.

For example, solutions containing sodium bromite or a mixture of sodium bromite and sodium hypobromite, as prepared by the method described in the applicants patent application Ser. No. 654.041, filed April 19, 1957, the solutions being adjusted to the desired bromine concentration before use, are particularly suitable for the pur' poses of the present invention. It is quite practicable to add to de-sizing solutions containing bromite and/or hypobromite according to the invention, suitable proportions of oxidation-resistant wetting agents in order to promote rapid penetration into the fabric.

The de-sizing operation is performed in an alkaline medium, with the initial pH of the solution being preferably within an approximate range of from 9 to 10.5. The appropriate pH conditions may be obtained, for example, by adding soda. The addition of a buffer, while feasible, is not essential since a slight drop in pH during the operation is not objectionable. As a general rule however, the operating conditions should be maintained such that, throughout the operation, the pH will not drop to such an extent as to cause a formation of free bromine which would attack the cellulose material and would impair the characteristics of the fabric.

The time of treatment will depend, for a given type of fabric, on the concentration of reagent in the solution. A quick pass of the fabric through a more concentrated solution makes it possible to achieve as efiicient a desizing operation than a longer dwell in less concentrated solutions. The results indicated in the table given above show, for example, that full size removal is obtained within 80 minutes when using a bromite solution containing 1 gram available bromine per liter, and within 15 minutes with a solution containing 2 grams available bromine per liter.

The above data result from laboratory tests and hence their value is comparative rather than absolute. Thus, for a given fabric treated under comparable conditions, the indicated data clearly show the wide range over which the two interdependent factors, time and reagent concentration, may be varied without impairing the final result. This feature is an outstanding advantage of the present invention since the process is thus seen to possess high flexibility for performance on a commercial scale and may be carried out by the use of various procedures and with various types of plant.

For example, the treatment may be conducted in a jigger-type apparatus containing a de-sizing solution, with the fabric being fed therethrough. In such apparatus the direction of feed may be reversed by reversing the operation of the machine, thereby repeating the process. The machine likewise permits varying the reaction time of the fabric in the bath, e.g. between a few minutes and one hour. The treatment time and the concentration in the solution are predetermined in accordance with the nature and texture of the material being treated. Good results have been obtained, for instance, including a treatment time less than one hour, when poplin is treated at ordinary temperature in a solution wherein the concentration is no more than 5 grams active bromine per liter of hypobromite, or 2 grams available bromine per liter of bromite. The above indicated time may even further be reduced by increasing the concentration of the solution.

Another and extremely advantageous form of the invention is to apply the so-called pressing or fulling process. In this process the material is passed at a very high rate (e.g. 30 to 40 meters per minute) through a, bath of the solution, and is pressed at the outlet from the bath between two presser rollers. Since the fabric dwells for only a very short time in the reagent bath in this process, more highly concentrated solutions are generally used than when using a jigger. Thus, as compared to the concentrations mentioned above for the jigger process, satisfactory results have been obtained when treating the same poplin stock with solutions wherein the concentration is 10 grams (or less) available bromine per liter with the hypobromite solution, and 5 grams (or less) available bromine per liter with the bromite.

One outstanding advantage of the invention is to permit a continuous de-sizing treatment under extremely economical conditions. Owing to the use of reagents which are efiicient at ordinary temperature, the pressing method just mentioned, which was inapplicable with the reagents conventionally used heretofore, becomes feasible and may be applied without any additional operations. This procedure in particular avoids having to apply a steaming step as is required where the oxidizer used was sodium chloride or the like.

As compared to the processes using acids and enzymes, the invention has important advantages. Operation at ambient temperature considerably simplifies the necessary plant and lowers the over-all cost of the de-sizing operation. The operating time is considerably reduced. After a treatment not exceeding one hour, the fabric is in a condition to be subjected to the subsequent treatments without necessitating many hours of intermediate storage. Irregular de-sizing due to non uniform temperature during storage is also avoided in this way.

The use of bromite and/ or hypobromite has manifest advantages when the de-sizing operation is conducted as a preliminary stage preceding the remaining textile processing operations. According to the invention, the use of bromite has yet another important advantage. It has been found that bromite is stable in alkaline media at elevated temperatures and constitutes a highly efficient starch-oxidizing agent at temperatures definitely higher than ambient temperature even in highly alkaline media. Consequently the de-sizing may be effected by means of bromite during the scouring operation, thus eliminating one stage of treatment. In such a procedure, it is simply necessary to add to the conventional scouring bath, usually comprising a solution of soda and sodium carbonate, a relatively small amount of alkali bromite, particularly sodium bromite. As was the case for de-sizing at ordinary temperature, the amount of bromite to be used depends of course on the textile stock being treated. For example, it has been found that satisfactory results are had when treating a very tightly woven and heavily sized poplin in a scouring bath containing less than 1 gram per liter of available bromine per liter in the form of bromite (about 5 grams available bromine per kilogram fabric). The scouring step is performed in any of the conventional apparatus used for this purpose, and satisfactory results are obtained at the end of two hours treatment. Fabric thus treated is completely de-sized, has good hydrophilic characteristics and entirely satisfactory bleaching and dyeing characteristics.

It will be understood that the procedures described above were given as examples only, and that bromite and/or hypobromite solutions may be applied according to the invention in connection with any of various other de-sizing processes without exceeding the scope of the invention. Similarly the bromite may be added to scouring baths of any specific composition without exceeding the scope of the invention.

A few further non restrictive examples of specific procedures according to the invention are given below.

Example 1 Poplin stock initially containing 12.2% size is treated with a water solution of sodium bromite containing 5 grams available bromine per liter, and 5 cc. per liter of a wetting agent of the aryl-alkylsulfonamine type. The initial pH of the solution is 9.8.

The fabric is fulled broadwise at ordinary temperature in the above solution and is taken up at the outlet from the fulling press. Two passes through the bath are effected at a rate of about 30 meters per minute. The squeezing or pressing ratio is about 50 to 55%.

After this treatment which constitutes the de-sizing process proper, the fabric is washed in a dilute soda solution (5 grams NaOH per liter) at about 90 C. and is then passed directly to the scouring step.

Samples of the fabric thus treated are tested for the percentage of residual size on the warp yarn and this is found to be zero. Further tests indicate the high-quality characteristics of the resulting fabric.

Example 2 The fabric treated is the same as in Example 1. The solution used contains 1 gram available bromine per liter in the form of sodium bromite. 5 cc. per liter of a wetting agent are added, of a type similar to that used in Example 1. Solution pH is 9.7.

The fabric is treated in a jigger at ordinary temperature for 60 minutes by passing the fabric through the bath, provided in an amount of liters solution per kilogram of fabric. The fabric is then washed in dilute soda solution as in Example 1.

On analyzing the treating solution after the process, it was found that 2.5 grams available bromine had been used up per kilogram of the fabric. The starch was completely eliminated and the characteristics of the fabric were preserved.

Example 3 Calico containing about 8% size is treated in a jigger, with a solution containing 0.5 gram available bromine per liter, of which 43% are in the form of sodium hypobromite and 57% in the form of sodium bromite. The initial pH of the solution is 9.9. A wetting agent comprising a sodium salt and butylricinoleic ester sulfonate is added to this solution in an amount of 5 grams per liter to promote penetration of the reagent.

At the end of 60 minutes treating time at about C. in the above solution the material is washed in a heated soda solution containing 5 grams per liter.

Iodine test shows the starch was completely removed and the characteristics of the fabric entirely unimpaired.

Example 4 Poplin containing 12.2% size similar to that in Example 1, is treated in a scouring bath comprising a solution containing 15 g./l. NaOH, 15 g./l. Na CO and 0.5 g./l. available bromine as bromite. About 5 liters of this solution per kilogram fabric were used and the fabric boiled two hours while maintaining constant volume.

The fabric is then washed in hot water then rinsed in cold running water. The amount of residual size is determined in a sample of the treated fabric and the size is found to be completely eliminated. Tests show that the fabric has good hydrophilic properties and the other characteristics are retained.

What I claim is:

1. A method of removing starch size from cellulose textile fabric comprising oxidizing said size on said fabric in an aqueous alkaline medium having a pH value of at least about 9 with an oxidizing agent selected from the group consisting of alkali metal bromites, alkali metal hypobromites and a mixture of both for a sufficient time until starch is removed.

2. A method of removing starch size on said fabric from cellulose textile fabric comprising oxidizing said size in an aqueous alkaline medium having a pH value of at least about 9 with an oxidizing agent selected from the group consisting of sodium bromite, sodium hypobromite and a mixture of both for a sufiicient time until starch is removed.

3. A method of removing starch size from cellulose textile fabric comprising subjecting the said fabric to contact with an aqueous alkaline solution containing an oxidizing agent selected from the group consisting of sodium bromite, sodium hypobromite and a mixture of both and the said solution having a. pH' value in the range of from about 9 to about 10.5, the treatment being effected at room temperature until substantially complete removal of starchy materials is obtained.

4. A method of removing starch size from cellulose textile fabric comprising subjecting the said fabric to contact with an aqueous alkaline solution containing sodium bromite in a concentration of at most about 5 grams available bromine per liter and having a pH value in the range of from about 9 to about 10.5, the treatment being effected at room temperature until substantially complete removal of starchy materials is obtained.

5. A method of removing starch size from cellulose textile fabric comprising subjecting the said fabric to contact with an aqueous alkaline solution containing sodium hypobromite in a concentration of at most about 10 grams available bromine per liter and having a pH value in the range of from about 9 to about 10.5, the treatment being effected at room temperature until substantially complete removal of starchy materials is obtained.

6. A method of removing starch size from cellulose textile fabric comprising subjecting the sized fabric to contact with an aqueous alkaline scouring liquor having a pH value of at least about 9 wherein is added sodium bromite in amount of at most 1 g. active bromine per liter of said liquor and in proportion of from about 2.5 to about 5 grams available bromine per kilogram of dry treated fabric and maintaining boiling temperature for a period of time sufiicient to complete the scouring whereby the said fabric is simultaneously desized and scoured.

References Cited in the file of this patent UNITED STATES PATENTS 2,253,242 MacMahon Aug. 19, 1941 FOREIGN PATENTS 549,678 Great Britain Dec. 2, 1942 OTHER REFERENCES Radley: Mfg. Chemist & Mfg. Perfumer, July 1942, pp. 158-166 (copy in POSL). 

1. A METHOD OF REMOVING STARCH SIZE FROM CELLULLOSE TEXTILE FABRIC COMPRISING OXIDIZING SAID SIZE ON SAID FABRIC IN AN AQUEOUS ALKALINE MEDIUM HAVING A PH VALUE OF AT LEAST ABOUT 9 WITH AN OXIDIZING AGENT SELECTED FROM THE GROUP CONSISTING OF ALKALI METAL BROMITES, ALKALI METAL HYPOBROMITES AND A MIXTURE OF BOTH FOR A SUFFICIENT TIME UNTIL STARCH IS REMOVED. 